\documentclass{article}\begin{document}
\begin{theorem}
\declare{syntax={infix,7,"/",l}, meaning=artih1.divide}
$2+3$
$$2+5$$
\end{theorem}
\begin{proof}
\declare{macro=\asd, meaning=asdasd,    argspec=[2], code={...}}
$1+1$
\end{proof}
\begin{lemma}
$2+2$
\end{lemma}
\end{document}
